In the related art, there is a technique for collecting refrigerating machine oil that is discharged along with a refrigerant from a compressor in an air-conditioning apparatus that includes the compressor as one of element devices of a refrigeration cycle. In general, the amount of refrigerating machine oil to be sealed is uniformly set on the basis of an air-conditioning apparatus that includes the longest refrigerant pipe among air-conditioning apparatus in which refrigerating machine oil is expected to be sealed. In addition, an amount of refrigerating machine oil including an estimated amount of refrigerating machine oil to be deposited on a refrigerant pipe and the like is usually sealed in advance. Therefore, in practice, operations of air-conditioning apparatus are performed in a state where the amount of refrigerating machine oil is large. In particular, in the case of an air-conditioning apparatus that includes a refrigerant pipe that is short in length, there will be a large surplus of refrigerating machine oil.
Therefore, “a technology for calculating a surplus amount of refrigerating machine oil contained in a compressor on the basis of the length of a refrigerant pipe of a refrigerant circuit and opening an on-off valve of a connection pipe at predetermined time intervals in accordance with the surplus amount of the oil” has been proposed (see, for example, Patent Literature 1).